Added renderDay

[andrewmcd1]

This PR introduces a new prop, renderDay, to enhance the customization capabilities of react-native-calendar-picker. With this addition, users can now provide a custom component to render each day in the calendar according to their specific requirements.

Changes Introduced:

• Added a new prop named renderDay.
• This prop allows users to specify a custom component for rendering each day.
• Provides greater flexibility in styling and functionality customization for calendar components.
• Includes documentation updates to reflect the new prop and its usage.

Why is this change necessary?
The ability to customize the rendering of individual days in the calendar is a highly requested feature from our user community. By introducing the renderDay prop, we empower users to tailor the calendar's appearance and behavior to suit their unique application needs.

How to Use:
To utilize the new renderDay prop:

1. Import the react-native-calendar-picker component.
2. Pass a custom component to the renderDay prop, specifying how each day should be rendered.
3. Customize the rendering logic within the provided component to achieve the desired visual appearance and functionality.

This enhancement enriches the versatility of react-native-calendar-picker, empowering developers to create more tailored and engaging calendar experiences within their React Native applications.

[white-room]

any chance someone has had time to take a look at this?